There is a case to optionally design the shape of a housing for a swing-type optical system. For example, in a case of a flying object, the swing-type optical system to optically obtain target images is provided on the tip part of the flying object. In this case, an optical dome is provided on the tip part of the flying object, is formed by material which transmits through light beams having bandwidth to be received with the swing-type optical system, and protects the swing-type optical system. It is desirable that the shape of such an optical dome is designed in the view of the optics and the aerodynamics.
From the view of the optics, while incident light beams from the outside of the optical dome transmit through the optical dome, there is a desire for characteristic not to have an influence on this light as much as possible. In the view of this, when the swing-type optical system performs a swinging operation to obtain outside images from the inside of the optical dome and to change the direction of the eyesight for obtaining images, the following technique is known. In this technique, the shape of the optical dome is formed by the curved surface consisting of a part of the spherical surface in order to minimize a difference in refraction angle of the optical dome with dependence on the swing direction. Here, the swing direction means the direction of the light axis of the swing-type optical system and is determined by this swinging operation. That is, the central point of this spherical surface coincides with the central point of the swinging operation of the swing-type optical system, and the swing-type optical system has the same optical characteristic from the optical dome, even if the swing-type optical system obtains images from any direction. As a result, the optical influence that the swing-type optical system undergoes from the optical dome is restrained.
On the other hand, from the view of the aerodynamic, in the tip part of the flying object, the shape of so-called ogive is more favorable to the curved surface shape which consists of a part of above-mentioned spherical surface. FIG. 1A is a diagram showing an example of an ogive shape 10. FIG. 1B is a diagram showing an example of the definition of the ogive shape 10. In the examples shown in FIG. 1A and FIG. 1B, the ogive shape 10 is defined as the rotating body which is obtained by rotating the predetermined turning arc 12 around a rotation axis 11. The rotation axis 11 is a straight line which does not pass the center 13 of a circle belonging to the arc 12.
In a case that the optical dome has the ogive shape, this case differs from a case that the optical dome has a spherical shape or a part of the spherical shape, a refraction angle in the optical dome differs on the basis of position of incident light beams on the optical dome. This will be described by using an exemplary diagram.
FIG. 1C is a diagram showing an example with the optical characteristic of the optical dome of the ogive shape. FIG. 1C shows the optical dome 20 which shows a part of the optical dome, a first incident light beams 30, a first transmitted light beams 40, a second incident light beams 50 and a second transmitted light beams 60. The optical dome 20 has an outside surface 21 and an inner surface 22. The first incident light beams 30 have a first incident light beam 31, a second incident light beam 32 and a third incident light beam 33. The first transmitted light beams 40 contain a first transmitted light beam 41, a second transmitted light beam 42 and a third transmitted light beam 43. The second incident light beams 50 contain a fourth incident light beam 51, a fifth incident light beam 52 and a sixth incident light beam 53. The second transmitted light beams 60 contain a fourth transmitted light beam 61, a fifth transmitted light beam 62 and a sixth transmitted light beam 63.
The optical dome 20 has a so-called ogive shape. The direction of the rotation axis 11 of this ogive shape is hereinafter used as the reference direction. In the incident light beams 30 which are parallel light, the first incident light beam 31 to the third incident light beam 33 are parallel each other, and have angle θ2 to the reference direction. When the first incident light beams 30 are irradiated on the optical dome 20 from the outside of the optical dome 20, the first incident light beams 30 are refracted on the outside surface 21, moreover are refracted on the inner surface 22, then reach inside of the optical dome 20 as the first transmitted light beams 40. At this time, in the first transmitted light beams 40, the first transmitted light beam 41 to the third transmitted light beam 43 are not parallel each other anymore, that is, the first transmitted light beam 41 to the third transmitted light beam 43 lose parallelism. In the example shown in FIG. 1C, the first transmitted light beam 41 has angle θ2+f to the reference direction, the second transmitted light beam 42 has angle θ2+e to the reference direction and the third transmitted light beam 43 has angle θ2+d to the reference direction. Here, in general, the angles d, e, f are different respectively.
In the same way, in the incident light beams 50 which are parallel light each other, the fourth incident light beam 51 to the sixth incident light beam 53 have angle θ1 to the reference direction. When the second incident light beams 50 are irradiated on the optical dome 20 from the outside of the optical dome 20, the second incident light beams 50 are refracted on the outside surface 21, moreover are refracted on the inner surface 22, then reach inside of the optical dome 20 as the second transmitted light beams 60. At this time, in the second transmitted light beams 60, the fourth transmitted light beam 61 to the sixth transmitted light beam 63 are not parallel each other anymore, in the same way, the fourth transmitted light beam 61 to the sixth transmitted light beam 63 lose parallelism. In the example shown in FIG. 1C, the fourth transmitted light beam 61 has angle θ1+c to the reference direction, the fifth transmitted light beam 62 has angle θ1+b to the reference direction and the sixth transmitted light beam 63 has angle θ1+d to the reference direction. Here, in general, the angles a, b, c are different respectively.
This way, the ogive-shaped surface differs from the spherical surface or the curved surface which consists of the part of the spherical surface. When light beams transmits through the optical dome 20 having an optically symmetrically insufficient shape, by the various refracting phenomenon, even if incident light beams are parallel, there is a case that warp which the transmitted light beams are not parallel occurs, or there is a case that the warp differs in response to position which transmits through the optical dome 20. Furthermore, when the direction and the range of images which have been actually obtained as a result of a swinging operation by the swing-type optical system is called “direction of image obtainment”, the direction of the image obtainment differs from the swing direction which has been adjusted in response to the desired direction of image obtainment by the influence of the optical dome 20. Note that the term “direction of image obtainment” is also called “photographing direction”.
FIG. 1D is a diagram showing the configuration example of an image obtaining apparatus 110 which is used the optical dome of the ogive shape. The image obtaining apparatus 110 shown in FIG. 1D has a swing-type optical system 120 and an optical dome 140. A swing direction 130 of the swing-type optical system 120 is on the light axis of the swing-type optical system 120 when the swing-type optical system 120 is in a central position.
The swing-type optical system 120 performs a swinging operation mainly in fixed starting point. For example, the swing-type optical system 120 moves to position 121 or position 122 shown in FIG. 1D. The swing direction 131 of the swing-type optical system 120 is on the light axis of the swing-type optical system 120 when the swing-type optical system 120 is in the position 121. The swing direction 132 of the swing-type optical system 120 is on the light axis of the swing-type optical system 120 when the swing-type optical system 120 is in the position 122.
However, when light beams transmit through the ogive-shaped optical dome 140, parallelism is lost from incident light beams from the swing direction by the refracting phenomenon described in the FIG. 1C. The warp has occurred in obtained images by the swing-type optical system 120. Moreover, as referred to FIG. 1C, degrees of the refracting phenomenon differs in response to the swing direction and the characteristic of the warp also differs. In other words, one of the reasons that characteristic of the warp differs is that when the incident light beams transmit through the optical dome having curved surface shapes such as the ogive shape, angle (e.g., α shown in FIG. 1C) differs in response to the swing direction of the swing-type optical system. Here, the angle (α) indicates angle between the swing direction (e.g., D shown in FIG. 1C) of the swing-type optical system and the direction of the perpendicular line (e.g., L shown in FIG. 1C) in an intersection (e.g., I shown in FIG. 1C) on the outer surface 21.
In this way, when the shape of the housing for the swing-type optical system does not have enough optical symmetry, the correction optical system which corrects the image warp which occurs in response to a swing angle (e.g., θ1 shown in FIG. 1C) of the swing-type optical system is required. Here, it is possible to define the swing angle as angle between a light axis (namely, an optical axis of the swing-type optical system, e.g., D shown in FIG. 1C) and the predetermined reference direction (e.g., the rotation axis 11).
In relation to the above, Patent literature 1 discloses an optical apparatus. This optical apparatus has a photography optical system, image blur correction means, vibration detection means, signal generation means and control means. Here, the angular field of view of photography optical system is variable. The image blur correction means corrects the image blur which accompanies vibration. The vibration detection means detects vibration. The signal generation means generates a movement signal based on the output from the vibration detection means. The control means controls the image blur correction means based on the movement signal. The control means changes the characteristic of the signal generation means on the basis of the angular field of view of the photography optical system and the value of the image blur signal.
However the image blur correction means described in the patent literature 1 corrects the image blur which accompanies small vibration with photography optical system, and is not the one which corrects an image warp according to the axial change of the light of the photography optical system.